Evaluation of Modeled and 

Measured Energy Savings in 

Existing All Electric Public 

Housing in the Pacific Northwest 

Andrew Gordon, Michael Lubliner, Luke Howard, 

Rick Kunkle, and Emily Salzberg

BA-PIRC

April 2014
NOTICE

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iii

Evaluation of Modeled and Measured Energy Savings in Existing 

All Electric Public Housing in the Pacific Northwest

Prepared for: 

The National Renewable Energy Laboratory 

On behalf of the U.S. Department of Energy’s Building America Program

Office of Energy Efficiency and Renewable Energy 

15013 Denver West Parkway 

Golden, CO 80401 

NREL Contract No. DE-AC36-08GO28308 

Prepared by: 

Michael Lubliner, Andrew Gordon, Luke Howard, Rick Kunkle, and Emily Salzberg

Washington State University Extension Energy Office 

for 

Building America Partnership for Improved Residential Construction

1967 Clearlake Road 

Cocoa, FL 32922 

NREL Technical Monitor: Stacey Rothgeb 

Prepared under Subcontract No. KNDJ-0-40339-03 

April 2014 
iv

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v 

Table of Contents

Table of Contents........................................................................................................................................ v

List of Figures ............................................................................................................................................ vi

List of Tables .............................................................................................................................................. vi

Definitions.................................................................................................................................................. vii

Acknowledgments ................................................................................................................................... viii

Executive Summary................................................................................................................................... ix

1 Introduction and Background ............................................................................................................. 1

2 Scope and Purpose .............................................................................................................................. 3

3 House Description................................................................................................................................ 4

4 Energy Audits ....................................................................................................................................... 5

5 Modeling Methods ................................................................................................................................ 6

6 Billing Analysis Methods..................................................................................................................... 8

7 Results................................................................................................................................................. 10

7.1 Audits .......................................................................................................................................... 10

7.2 Temperature and Relative Humidity Monitoring ............................................................................ 13

7.3 Homeowner Surveys...................................................................................................................... 14

7.4 Modeling......................................................................................................................................... 15

7.5 Utility Billing Analysis ..................................................................................................................... 20

7.6 Utility Model and Energy Simulation Model Comparison............................................................... 25

8 Conclusions ........................................................................................................................................ 27

9 Recommendations ............................................................................................................................. 29

10 Potential Research Opportunities..................................................................................................... 30

References................................................................................................................................................. 31

Appendix A: Audit Forms......................................................................................................................... 32

Appendix B: Occupant Survey ................................................................................................................ 34
vi 

List of Figures

Figure 1. Salishan housing, prior to reconstruction ............................................................................... 1

Figure 2. Salishan 975-ft2 duplex (left), and 1,109-ft2 duplex (right) ...................................................... 4

Figure 3. Exhaust ventilation system controls ...................................................................................... 10

Figure 4. Monitored temperature, Salishan phases 1–6 ....................................................................... 13

Figure 5. Monitored RH, Salishan phases 1–6 ....................................................................................... 13

Figure 6. RH and temperature for monitored units in Salishan, November 2012 to March 2013 ..... 14

Figure 7. Breakdown by load type; 100% electric ................................................................................. 19

Figure 8. Breakdown by load type; 100% DHP....................................................................................... 19

Figure 9. Monthly aggregate electricity use for two-bedroom end units ............................................ 20

Figure 10. Monthly aggregate electricity use for three-bedroom end units ....................................... 21

Figure 11. Annual electricity use of each Salishan 1–7 housing units ............................................... 24

Unless otherwise noted, all figures were created by BA-PIRC.

List of Tables

Table 1. Salishan Phase 1–6 Envelope Specifications............................................................................ 4

Table 2. Salishan House Characterization................................................................................................ 6

Table 3. Salishan 1–6 Average Leakage Converted to ACH50 and SLA ................................................ 7

Table 4. Characteristics of Salishan Housing Units................................................................................ 8

Table 5. Utility Billing Analysis Comparison Groups.............................................................................. 8

Table 6. Salishan Fan Flow Rates ........................................................................................................... 11

Table 7. Envelope Leakage Testing Results .......................................................................................... 12

Table 8. Combined House Depressurization.......................................................................................... 12

Table 9. Salishan 1–6 BEopt Estimated Site Energy Consumption in kWh Annually........................ 15

Table 10. Calculated Occupancy for Two- and Three-Bedroom Units ................................................ 16

Table 11. BEopt Estimated Consumption Comparison, Two- and Three-Bedroom Units ................ 16

Table 12. Energy Usage and Cost Benefit of Retrofit Measures in Salishan 1–6............................... 18

Table 13. Regression Model Results for Each Comparison Group ..................................................... 23

Table 14. T-Test Results for Each Comparison Group ......................................................................... 25

Table 15. BEopt Model Compared to Utility Regression Model ........................................................... 26

Table 16. BEopt Model Compared to Utility Regression Model, Base Load, and Heating Load ...... 26

Unless otherwise noted, all tables were created by BA-PIRC.
vii 

Definitions

ACH50 Air changes per hour at 50 Pascals

ASHRAE American Society of Heating, Refrigerating and Air-Conditioning Engineers

BEoptTM Building Energy Optimization software

CFM50 Cubic feet per minute at 50 Pascals

DHP Ductless heat pump

ELA Effective leakage area

EqLA Equivalent leakage area

ERV Energy recovery ventilation

HPWH Heat pump water heater

KCHA King County Housing Authority

LEED Leadership in Energy and Environmental Design

MEL Miscellaneous electric load

RH Relative humidity

THA Tacoma Housing Authority

TPU Tacoma Public Utilities

VIAQ Washington State Ventilation and Indoor Air Quality Code

WSEC Washington State Energy Code

WSU Washington State University Energy Program
viii

Acknowledgments

This work is sponsored in large part by the U.S. Department of Energy Building Technologies 

Office Building America Industrialized Housing program under cooperative agreement DEFC36-99GO10478. 

The authors would like to thank the following persons and organizations for their contributions 

to this project and paper: Eric Martin, Building America; Ken Eklund and David Hales, 

Washington State University Energy Program (WSU); Bruce Carter, Tacoma Public Utilities 

(TPU); Derek Johnson, Walsh Construction; Theresa Weston, DuPont; Don Stevens, Panasonic 

USA; Gary Nelson and Collin Olson, Energy Conservatory; Roberta Schur, Tehani Bowman, 

Barbara Pearsall, and other Tacoma Housing Authority staff.
ix

Executive Summary

This project evaluates market-ready energy solutions to improve the efficiency of affordable 

housing for new and existing (built since 2001) affordable housing in the marine climate of 

Washington State. 

The project analyzes the cost effectiveness of energy savings measures installed by a large public 

housing authority in Salishan, a community in Tacoma, Washington. 

The previous, first year report focused on the last of seven phases of construction (referred to as 

Salishan 7 in this report), which integrated energy efficiency technologies including a “hybrid” 

heating system, with a ductless heat pump (DHP) providing heat to the first floor, electric 

resistance heaters providing heat to the bedrooms, and increased envelope insulation (Gordon, 

Lubliner, Howard, & Kunkle, 2013). 

This report focuses on the modeled and measured energy usage of the first six phases of 

construction (referred to as Salishan 1–6 in this report), and compares the energy usage of those 

phases to phase 7. 

Building America researchers conducted detailed audits of eight dwelling units in the Salishan 

community, representative of each of the first six phases of construction. The goal of the audits 

was to conduct visual inspections of the homes, perform envelope leakage and ventilation system 

flow testing, and conduct occupant surveys. 

A typical Salishan duplex (975 ft2

) was modeled to the 2006 Washington State Energy Code 

(WSEC—the code in place at the time of construction) using BEopt version 1.4, to predict the 

energy usage for Salishan Phases 1–6 (to be compared to the billing analysis). 

Researchers conducted a billing analysis of all 631 housing units in Salishan, phases 1–7. The 

purpose of the billing analysis was to compare Salishan phases 1–6 built to WSEC with electric 

baseboard heat to the more efficient units in Salishan phase 7. 

This report focuses on the following primary Building America research questions: 

1. How does the modeled energy use (using Building Energy Optimization Software 

[BEopt]TM) for Salishan phases 1–6 compare to the actual use derived from billing data?

Total modeled energy usage for Salishan phases 1–6 was 11,922 kWh/year, with 3,544 

kWh/year for heating, or 29% of total energy usage. 

The billing analysis suggests annual energy use of the two-bedroom duplex (comparable to 

the unit modeled with BEopt) to be 12,088 kWh, with 5,091 kWh from heating. While the 

BEopt model and utility billing analysis yielded good alignment overall (a difference of 166 

kWh or 1.37% for total energy use), the heating load estimates were not well aligned, with a 

difference of 1,469 kWh or 21%, suggesting that this BEopt analysis may be overpredicting 

base load and underpredicting heating load. 

2. How does the annual energy usage of phases 1–6 compare to phase 7? 
x

A comparison of annual energy usage (from billing analysis) between Salishan phases 1–6

and Salishan 7 indicates savings of 1,400 to 4,300 kWh/year, a strong indicator of the 

benefits from the Salishan 7 energy efficiency improvements. 

3. What are the opportunities for energy efficiency retrofit improvements in Salishan phases 1–

6?

The energy efficiency and economic impact of mechanical upgrades were evaluated for 

Phases 1–6 (these phases were energy code compliant at the time of construction) as possible 

retrofit options. Given the fairly efficient building envelopes required under WSEC at the 

time of construction, evaluations focused on mechanical upgrades—specifically DHPs and 

heat pump water heaters (HPWHs).

If 100% of the existing electric resistance heating is assumed to be provided by the DHP, 

energy savings is predicted to be 2,602 kWh annually; this amounts to $193 in cost savings, 

and a 15-year payback (well within the expected life of the equipment). If the displacement 

level of the electric resistance heating is less than 100%, the savings and payback are 

reduced. Based on DHP retrofit research conducted in the Pacific Northwest (used in 

previous Building America projects), these savings may be reduced by as much as 60%. 

Researchers believe that displacement assumptions need additional investigation. Regardless 

of the displacement assumption, the installation of DHPs may be justified for units with a 

high heating load, where tenants have expressed strong dissatisfaction with comfort, or where 

there is a need for cooling (elderly tenants, or those with medical problems.)

The analysis of HPWHs suggests annual savings of 778 kWh, or $58. Using current 

incremental cost assumptions, payback for the HPWH does not fall within the useful life of 

the system. However, the installation of HPWHs may be justified for homes with high base

load use and high occupancy (a surrogate for high domestic water heating usage). Combining 

the installation of HPWHs and DHP retrofits may improve cost effectiveness and installation 

logistics in occupied dwellings.

4. How do the mechanical ventilation systems perform compared with Washington Statemandated requirements and ASHRAE 62.2-2010, and how did field assessments and 

occupant surveys reflect the operation of the systems?

Researchers determined that all eight dwelling units that received audits had ventilation 

systems capable of meeting Washington State Ventilation and Indoor Air Quality Code or 

ASHRAE 62.2-2010 requirements (in terms of fan flow), though runtimes varied. None of 

the tenants seemed to have a working knowledge of their ventilation systems.

5. What are the measured temperature and relative humidity (RH) levels in the homes during 

the heating season, and what impact did they have on occupant comfort?

Researchers installed HOBO temperature and RH data loggers at the time of the field audits; 

monitoring took place during the heating season 2012–2013 (November 2012 through March 

2013.) Average hourly indoor temperatures were 73°F for the monitoring period. The 

monitoring data do suggest high temperature swings in each home (as much as 31°F 
xi

difference between minimum and maximum monitored temperatures). Occupant surveys 

indicated a high degree of variability of satisfaction with the comfort levels in their homes; 

the high degree of variability in the monitored temperatures further reflects this.

Average hourly RH levels were 40% for the monitoring period, reflecting good humidity 

control with well operating whole-house fans and with air change rates typical for new 

construction (5–7 ACH50).

Building America researchers believe that additional research is warranted in the proper 

modeling of “hybrid” DHP/electric resistance heating systems, and displacement assumptions for 

DHP load in such a system.
1

1 Introduction and Background

Salishan is a mixed-income neighborhood of Tacoma, Washington, originally built by the federal 

government in 1942 to provide worker housing to support the war effort. The Tacoma Housing 

Authority (THA) managed Salishan for the federal government until the war’s end, and 

afterward, when the federal government gave most of Salishan, with about 880 apartments on 

188 acres, to THA to own and manage as a public housing community. Since construction, 

Salishan has been an important part of the City’s stock of affordable housing; in addition, it has 

served as a gateway—a first home for new immigrants.

By the end of the 1990s, the condition of the housing in Salishan was very poor. At the time of 

construction, long-term durability was not a high priority. In addition, the buildings were not 

well maintained and were falling apart.

Figure 1. Salishan housing, prior to reconstruction

From 2001 to 2011, THA undertook a $225 million effort, to demolish and reconstruct Salishan 

in seven phases. New Salishan is a mixed-use neighborhood of affordable and market-rate rental 

units, single-family homes for sale, commercial buildings, and parks, all on new infrastructure

(Tacoma Housing Authority, 2009).

In late 2009, Washington State University Energy Program (WSU) began working with THA, 

Walsh Construction, Tacoma Public Utilities (TPU), and consultant O’Brien and Company on 

the design, construction, and commissioning of phase 7 of the Salishan development.

Phase 7, which began construction in late 2009, and was completed in late 2010, is composed of 

91 low-income housing units built to ENERGY STAR® standards, and is the first federal Hope 

VI project to achieve Leadership in Energy and Environmental Design (LEED) Platinum.
2

Whereas previous phases were heated by electric baseboard units (one in each bedroom, two in 

the living room), Salishan 7 homes included ductless heat pumps (DHPs) (first floor, with 

baseboards in the bedrooms). In addition, the phase 7 units included improved insulation in the 

slab perimeter, walls, and ceiling. The previous, first year report focused on phase 7 (referred to 

as Salishan 7 in this report) (Gordon, Lubliner, Howard, & Kunkle, 2013).
3

2 Scope and Purpose

This report focuses on the modeled and measured energy usage of the first six phases of 

construction (referred to as Salishan 1–6 in this report), and compares the energy usage of those 

phases to phase 7.

The benefit of this research is to provide low-income housing organizations with analysis of 

market-ready energy efficiency solutions that can improve the efficiency of new housing stock, 

and identify cost-effective opportunities for retrofits of existing homes when appropriate.

Building America researchers conducted detailed audits of eight dwelling units in the Salishan 

community, representative of each of the first six phases of construction. The goal of the audits 

was to conduct visual inspections of the homes, perform envelope leakage and ventilation system 

flow testing, and conduct occupant surveys.

A typical Salishan duplex (975 ft

2

) was modeled to the 2006 Washington State Energy Code 

(WSEC—the code in place at the time of construction) using Building Energy Optimization 

software (BEopt) version 1.4, to predict the energy usage for Salishan Phases 1–6 (to be 

compared to the billing analysis).

Researchers conducted a billing analysis of all 631 housing units in Salishan, phases 1–7. The 

purpose of the billing analysis was to compare Salishan phases 1–6 built to WSEC with electric 

baseboard heat to the more efficient units in Salishan phase 7. 

This report focuses on the following primary Building America research questions:

1. How does the modeled energy use (using BEopt) for Salishan phases 1–6 compare to the 

actual use derived from billing data?

2. How do phases 1–6 compare to phase 7?

3. What are the opportunities for energy efficiency retrofit improvements in Salishan phases 1–

6?

4. How do the mechanical ventilation systems perform compared with Washington Statemandated requirements and ASHRAE 62.2-2010, and how did field assessments and 

occupant surveys reflect the operation of the systems?

5. What are the measured temperature and relative humidity (RH) levels in the homes during 

the heating season, and what impact did they have on occupant comfort?
4

3 House Description

The duplexes are mirrored floor plan, 1,109-ft2 and 975-ft2, two-story, two-bedroom, 1.5-bath 

units with a common wall separation. The homes are frame construction with trussed attics and 

perimeter insulated slab-on-grade floors. These homes were all built under the prescriptive 

requirements of the 2003 or 2006 WSEC (Table 1). Bedrooms are located on the second floor.

Figure 2. Salishan 975-ft2 duplex (left), and 1,109-ft2 duplex (right)

Table 1. Salishan Phase 1–6 Envelope Specifications

Code Vertical 

Glazing

Door 

U-Factor Ceiling Wall Above Grade

Slab 

on Grade

2003 WSEC 0.40

0.2 R-38 R-21 R-10

2006 WSEC 0.35

All units are heated with individual thermostatically controlled baseboard heaters, located in both 

bedrooms and the first-floor living room. Domestic hot water is provided by electric tank water 

heaters (50 gal) located within the conditioned space.

Whole-house ventilation is provided by a continuously operating exhaust fan located in the firstfloor laundry closets of all units. All duplexes have eight or nine dedicated fresh air intakes per 

dwelling unit. These intakes are operable trickle vents integrated into the frames of windows 

located in the kitchen, living room, bedrooms and upstairs bathroom. All whole-house 

ventilation systems are controlled by 24-h pin timers capable of running automatically or 

manually with a manual override function.
5

4 Energy Audits

In October of 2012, WSU conducted detailed audits of eight dwelling units in the Salishan 

development, in order to provide inputs for the modeling effort.

At least one dwelling unit was audited in phases 1–6 of the development. The dwelling units 

audited were nearly identical in floor plan to each other and those previously audited and 

reported on in Salishan 7 (Gordon, Lubliner, Howard, & Kunkle, 2013).

The audit protocol was consistent with the Residential Energy Services Network’s Quality 

Assurance Standard (RESNET, 2013). Each audit included:

• Blower door testing, utilizing The Energy Conservatory’s TECTITE software (The 

Energy Conservatory, 2012)

• Flow rate measurement of whole-house and spot ventilation

• Confirmation of basic home features, including area takeoffs and appliance, heating, 

ventilation, and air conditioning, and lighting information.

Above and beyond the standard quality assurance protocols, researchers conducted assessments 

of window trickle vents (fresh air intakes) and conducted worst-case depressurization tests of all 

exhausting fans and appliances (not typically indicated as there are no combustion appliances 

present in these homes.)

A blank audit form is included in Appendix A.

In addition, researchers administered a survey to the occupants of four of the homes (Phases 2, 3 

[two homes] and 6), to assess the occupancy patterns and other factors that might affect 

electricity use. A copy of the survey is included as Appendix B.

During the audits, Onset HOBO data loggers were installed in each of the eight units. The data 

loggers recorded temperature and RH levels at hourly intervals beginning on November 1, 2012 

through March 27, 2013.
6

5 Modeling Methods

The purpose of the energy simulation modeling is to compare the predicted energy use to the 

utility usage for Salishan Phases 1–6 built to the WSEC and Salishan Phase 7 built with 

improved thermal performance and DHPs. Additionally, the energy efficiency and economic 

impact of mechanical upgrades were evaluated for Phases 1–6 as possible retrofit options. 

Researchers used BEopt version 1.4 for estimation of energy performance of all Phases (National 

Renewable Energy Laboratory, 2013). Modeling evaluated the predicted performance of:

• Homes built in phases 1–6 to the 2003 and 2006 WSEC

• Homes built in phase 7 with improved envelope and mechanical equipment performance

• Homes built in phases 1–6, with additional energy efficiency mechanical upgrades.

The Salishan housing units modeled are the duplex floor plans, with square footage of either 975 

or 1,109 ft2 of conditioned floor area. The homes’ envelope and performance parameters in all 

seven phases for modeling purposes are specified in Table 2.

Table 2. Salishan House Characterization

Phase 1, 2, 3 4, 5, 6 7

Code 2003 WSEC 2006 WSEC 2009 WSEC

Square Footage 1,109/975 1,109/975 1,109/975

Number of Bedrooms 2 2 2

Vertical Glazing 0.40 0.35 0.30

Door U-Factor 0.20 0.20 0.20

Ceiling Insulation R-38 R-38 R-49 Advanced*

Wall Above Grade R-21 R-21 R-23

Slab on Grade R-10 R-10 R-15

Space Heating Electric baseboards Electric baseboards DHP

Thermostat Set Points 71°F Heating 71°F Heating 71°F Heating

76°F Cooling

Water Heating 0.95 Energy factor 0.95 Energy factor 0.95 Energy factor

Lighting 50% Compact 

fluorescent lamps

50% Compact 

fluorescent lamps

100% Compact 

fluorescent lamps

Dishwasher ENERGY STAR ENERGY STAR ENERGY STAR

Exhaust Fan ENERGY STAR ENERGY STAR ENERGY STAR

* Full insulation depth at heel

Envelope leakage rates used for modeling Salishan units from phases 1–6 are based on field air 

leakage testing with the fresh air window inlet vents in the position that the homeowners 

typically maintain and were found during the field audits. The average envelope leakage rate 

found through field audits was 953 CFM50 for the eight units audited from Salishan 1–6. The 

lowest tested leakage rate was 792 CFM50 and the highest was 1,144 CFM50. The 1,144 CFM50

unit had two windows that could not be closed securely due to data cables that passed through 

the windows and could not be disconnected according to requirements by the data provider. As 

such, an adjusted average was calculated taking the 1,144 CFM50 leakage rate unit out of the 
7

envelope leakage range; 926 CFM50 is the adjusted average used in the energy simulation 

modeling for Salishan 1–6. Table 3 lists leakage rates expressed as air changes per hour (ACH) 

at 50 Pascals and specific leakage area (SLA) for both the larger and smaller units.

Table 3. Salishan 1–6 Average Leakage Converted to ACH50 and SLA 

Conditioned Floor Area 1,109 ft2 975 ft2

CFM50 926 926

ACH50 5.9 6.7

SLA 0.00032 0.00036

There is little difference in the efficiency of building components required under the WSEC in 

the two energy code versions that Salishan 1–6 was built under (2003 and 2006), and likewise 

little difference in the efficiency of building components in each phase of construction as built 

prior to phase 7. As shown in Table 2, Vertical glazing U-factor is the differentiating factor 

among the first six phases of construction. As such, no discussion will take place in this paper 

regarding the incremental cost to meet the efficiency of the 2003 WSEC and the 2006 WSEC. 

The incremental costs for all energy efficiency improvements in Salishan 7 (noted in the first 

year report) were $6,064 (Gordon, Lubliner, Howard, & Kunkle, 2013). 
8

6 Billing Analysis Methods

The purpose of the utility bill analysis is to compare the housing units in Salishan phases 1–6

built to WSEC with electric baseboard heat to the units in Salishan phase 7. TPU provided 

monthly utility data1 for all 631 housing units in Salishan 1–7. The Salishan housing units are 

single-family, duplexes, triplexes, and fourplexes (Table 4). Two- and three-bedroom duplexes 

and triplexes are most common. There is a common set of floor plans and square footage is 

similar for units with the same number of bedrooms. For example, most two-bedroom units are 

between 970 and 1,145 ft2 and most three-bedroom units are between 1,224 and 1,373 ft2. 

Table 4. Characteristics of Salishan Housing Units

Type Single Duplex Triplex Fourplex Total

Bedrooms 3 5 1 2 3 4 2 3 2 –

Salishan 1–6 14 8 22 113 161 36 59 79 48 540

Salishan 7 2 1 4 18 14 4 12 24 12 91

The duplexes are side-by-side with one common wall. The triplexes are also side-by-side (row 

houses) with two end units (with one common wall) and an interior unit (with two common 

walls). The fourplexes are stacked units with two upper units and two lower units. These units 

have one shared wall and a shared floor/ceiling. 

For the purposes of the utility billing analysis, comparisons between Salishan 1–6 and Salishan 7 

are based on the housing unit location and number of bedrooms. Researchers compared end units 

for duplexes and triplexes with two and three bedrooms, interior units (triplexes) with three 

bedrooms, and stacked units (fourplexes) with two bedrooms. The majority of units are two- and 

three-bedroom end units (Table 2), so the analysis focuses on those units. Researchers did not 

consider the single-family and one-, four-, and five-bedroom units and interior two-bedroom 

units because there are so few of those units.

Table 5. Utility Billing Analysis Comparison Groups

Position Single End Interior Stacked Total

Bedrooms 3 5 1 2 3 4 2 3 2 –

Salishan 1–6 14 8 22 153 213 36 19 27 48 540

Salishan 7 2 1 4 28 28 4 2 10 12 91

The monthly utility data provided by Tacoma Public Utilities go back until the end of 2008, but 

some of the Salishan 7 units were not occupied until the end of 2010 or early 2011 (Gordon, 

Lubliner, Howard, & Kunkle, 2013). To allow for stable occupancy, this analysis focuses on the 

most recent 12-month period of utility data, which covers December 2011 to November 2012 

(referred to here as 2012). Researchers used two approaches to analyze the data:

• Monthly Aggregate Analysis: For each comparison group, the average electricity use for 

each month is calculated. Very low use is screened from the averages to attempt to 

 1 The actual billing periods do not correspond to calendar months, but the TPU data system allocates billing data to 

calendar months, which greatly simplifies the analysis.
9

remove cases where a unit may not have been occupied. This analysis essentially creates 

a “prototype” for each comparison group of typical monthly energy use. The monthly 

electricity use profiles are compared and a linear regression of electricity use and degree 

days is conducted to estimate base load and space heat electricity use for each prototype 

comparison group.

• Annual Analysis: The annual electricity use for each housing unit from December 2011 

to November 2012 is calculated. Housing units that have very low use in any particular 

month are screened out to remove cases where the unit may not have been occupied for 

the year. The difference in electricity use between the comparison groups is analyzed and 

the statistical significance is determined. 
10

7 Results

7.1 Audits

As noted above, the duplexes are equipped with dedicated fresh air intakes integrated into the 

frames of windows located in the kitchen, living room, bedrooms, and upstairs bathroom. During 

the audits, the position of these vents varied. Two homes were found with all the trickle vents 

closed, three homes had eight of nine closed, one home had seven of eight closed, one home had 

six of nine closed, and one home had four of nine vents in the closed position. The homeowner 

survey showed that occupants were not adjusting the position of these vents. In many of the 

units, opening of windows was used as a strategy for providing fresh air exchange when the 

weather was conducive to do so.

Per the Washington State Ventilation and Indoor Air Quality (VIAQ) code, homes using exhaust 

whole-house ventilation systems that do not have ducted space conditioning systems, must 

provide dedicated fresh air inlets to each habitable space. These fresh air inlets must provide no

less than 4 in.2 of net free area per habitable space (Washington State Building Code Council, 

2009) . As defined by code, the duplexes had four habitable spaces (living and dining rooms, and 

two bedrooms).

Ventilation system controls were located high on the wall in the laundry closet. These controls 

were readily accessible but were not labeled as whole-house ventilation controls. Most controls 

were programmed to run for 8 h/day, which is the VIAQ code minimum daily runtime. These run 

cycles were predominately dispersed in 2-h blocks and 4 h apart. However, one fan was programmed to run for 23 h/day while two others were programmed to run for 4.5 h/day and 5 h/day.

Figure 3. Exhaust ventilation system controls

Whole-house exhaust fan flow rates in all units were measured for flow with a commercially 

available flow capture hood (Balometer Junior, manufactured by Alnor), for an average of 

72 CFM; flow rates ranged from 54 to 90 CFM (see Table 6 for individual fan flow rates and 

runtimes). This is more than their listed rate of 57 CFM (at 0.25 in. water column), and well 

exceeding the VIAQ code minimum requirement of 45 CFM systems running a minimum of 

8 h/day.
11

Table 6. Salishan Fan Flow Rates

Dwelling Unit Salishan 1 Salishan 2 Salishan 3a Salishan 3b Salishan 4 Salishan 5a Salishan 5b Salishan 6

Whole-House Fan 

Flow (CFM) 54 90 87 87 60 62 62 69

Runtime 5 h 5 h 8 h 8 h 40 min 8 h 8 h 8 h

VIAQ CodeCompliant Flow Rate

55 min 

82 max

60 min 

90 max

55 min 

82 max

55 min 

82 max

60 min 

90 max

55 min 

82 max

55 min 

82 max

55 min 

82 max

62.2-2007-Compliant 

Flow Rate

45 45 45 45 45 45 45 45

Downstairs Bath 33 48 78 71 Not 

functional No data 78 56

Upstairs Bath 49 9 45 60 No data No data 60 60

Kitchen Fan Functional Functional Functional Functional Functional Functional Functional Functional
12

Air leakage testing was performed on all eight homes audited using The Energy Conservatory 

blower door test equipment and software (TECTITE). Blower door tests were conducted in three 

configurations—with window vents open, closed and as found. Results of these tests are shown 

in Table 7. Estimates of the homes’ trickle vent net free areas were derived from these tests and 

are also shown in Table 7. This estimate roughly equates to the VIAQ codes minimum 

requirement (16 in.2) for fresh air intakes in the majority of these homes.

Table 7. Envelope Leakage Testing Results

Dwelling 

Unit

CFM50

Vents as 

Found

CFM50

Vents 

Open

CFM50

Vents 

Closed

CFM50

Vents*

ACH50 

Vents 

Closed

Est. Vent 

Net Free 

Area (in.2)

# of 

Vents

Salishan 1 792 887 729 158 5.28 15.8 9

Salishan 2 862 1,011 862 149 5.5 14.9 9

Salishan 3a 986 1,006 919 87 6.6 8.7 9

Salishan 3b 926 1,074 899 175 6.4 17.5 9

Salishan 4 1,144 1,282 1,098 184 7.0 18.4 9

Salishan 5a 957 1,063 957 106 6.9 10.6 8

Salishan 5b 980 1,070 980 90 7.1 9.0 8

Salishan 6 976 unknown 960 unknown 7.0 unknown 8

*Difference between vents open and vents closed.

Although none of the homes at Salishan 1–6 were built with combustion appliances, they were 

all tested to determine the effect exhaust fans had on house pressure with reference to the 

outdoors when activated. Table 8 represents the average house depressurization with reference to 

outside with the introduction of each exhaust ventilation system starting with the whole-house 

fan.

The ambient conditions during the times of testing were windy (gusts > 20 mph); therefore, data 

were recorded for only four of the homes tested. Of these homes, the low end of depressurization 

with all exhaust appliances on was –9.2 Pascals. The greatest depressurization under these 

conditions was –13.3 Pascals. With only the whole-house fan on, maximum depressurization was 

–2. However, the whole-house fan depressurization data were well below the normal fluctuation 

induced by exterior wind conditions. All pressures were taken over a 30-s average.

Table 8. Combined House Depressurization

House Depressurization With Reference to Outside

Fresh Air Intake Closed (Pascals)

Average High Low

Baseline –1.2 –1.8 1.7

Whole-House Fan –1.8 –2 –0.8

+ Dryer –3.1 –3.4 –2.7

+ Kitchen Range Fan on HIGH –7.5 –8.6 –5.9

+ First-Floor Bath Fan –9.2 –11 –7.3

+ Second-Floor Bath Fan –11.2 –13.3 –9.2
13

7.2 Temperature and Relative Humidity Monitoring

The average indoor temperature for the eight units monitored was 73°F for the monitoring 

period. Temperature and RH distributions for all eight units are shown in Figure 4 and Figure 5.

Figure 4. Monitored temperature, Salishan phases 1–6

Figure 5. Monitored RH, Salishan phases 1–6

RH monitoring results are also shown in Figure 6, along with minimum, maximum, and average 

temperatures in each unit. The RH data require some explanation—the colored lines represent 

the frequency of RH values at or above specific bin values. For example, the purple line 

represents the frequency of RH values at or above 50%; the y-axis indicates the percentage of the 

monitoring period that the hourly average RH monitoring data meet or exceed that number.

50

55

60

65

70

75

80

85

90

95

Nov-12 Dec-12 Jan-13 Feb-13 Mar-13

Temperature (°F)

0

10

20

30

40

50

60

70

Nov-12 Dec-12 Jan-13 Feb-13 Mar-13

Humidity (%)
14

0%

10%

20%

30%

40%

50%

60%

70%

5b 3b 5a 4 2 6 1 3a

% of Time That % RH is Equal or Greater Than

Heating Season (November 2012 to March 2013)

65% RH

60% RH

55% RH

50% RH

Temp. Min 53°F 63°F 61°F 63°F 61°F 59°F 63°F 65°F

Temp. Max 84°F 83°F 85°F 88°F 83°F 79°F 74°F 83°F

Temp. Avg 69°F 73°F 75°F 76°F 71°F 71°F 69°F 75°F

Figure 6. RH and temperature for monitored units in Salishan, November 2012 to March 2013

As shown in Figure 6, the monitoring data do suggest high temperature swings in each home (as 

much as 31°F difference between minimum and maximum monitored temperatures). Occupant 

surveys indicated that all tenants were dissatisfied with the uneven distribution of heat in their 

home; the high degree of variability in the monitored temperatures further reflects this. It should 

be pointed out that researchers had no means of associating low temperature readings with 

periods of no occupancy, but the homeowner surveys (see Section 7.3, below) indicate that the 

units were occupied much of the time.

Average RH levels were 40% for the monitoring period, suggesting good humidity control with 

well operating whole house fans and envelope leakage rates between 5 and 7 ACH50 (typical for 

new construction). As shown in Figure 6, one home (Salishan 1) experienced high humidity 

during the monitoring period. This home had no working dryer, and the tenants were drying 

clothes inside the home.

7.3 Homeowner Surveys

The results of the homeowner surveys are summarized below.

• With the exception of one home (Salishan 6) containing a chest freezer, there were no 

unusual electrical loads in any of the homes.

• All homes were occupied by two full-time adult occupants except for one of the phase 3 

homes, which had one adult full-time occupant. All homes were occupied by at least one
15

occupant for 96% of the hours of the week and none of the homes were occupied by 

anyone spending more than 20 h outside the home for work or school. The phase 2 home 

rarely had visitors, whereas the other three homes frequently had daytime and evening 

guests.

• Homeowners had limited knowledge of the presence and operation of the ventilation 

system. All but one air inlet vent was found to be in the closed position in all but the 

phase 3 homes, which had four and nine vents open. None of the homes’ whole-house 

ventilation controls were labeled as required by code. 

• None of the occupants surveyed commented that they noticed any negative or positive 

effects of the ventilation system. Operable windows were used in all homes during 

favorable weather in order to allow intake of fresh air. Window trickle vents were never 

adjusted by occupants of any surveyed homes. Moisture-related issues were not observed.

• There was no use of air conditioners in any of these homes.

• Occupant control of the thermostat varied. Two of the homes’ occupants (phase 3 [one 

home] and phase 6) set the thermostat and left it there for the duration of the heating 

season. The phase 2 home’s occupants left the downstairs thermostat in one position for 

the entire heating season but varied the upstairs thermostats upon demand. The other 

phase 3 home’s occupants adjusted thermostats often and dramatically.

The homeowners were either very satisfied or very dissatisfied the energy efficiency and comfort 

of their homes. However, there was commonality in that they were all dissatisfied with the 

uneven distribution of heat throughout the home. This may be due to the occupant control issues 

noted above; the occupant may have to make continual adjustments to the thermostat to achieve 

comfort.

7.4 Modeling

The results of the energy simulation modeling for Salishan 1–6 are detailed in Table 9 and 

include units built to the 2003 and 2006 WSEC for the two different floor plans based on square 

footage. The highest usage model is the larger of the two floor plans built to the earlier 2003 

energy code. Predictably, the lowest usage model is the smaller of the two floor plans built to the 

subsequent 2006 energy code. The difference in estimated usage between these two models is 

1,360 kWh annually. 

Table 9. Salishan 1–6 BEopt Estimated Site Energy Consumption in kWh Annually

975-ft2 Model 1,109-ft2 Model

2003 Code 2006 Code 2003 Code 2006 Code

Miscellaneous Electric Loads (MELs) 5,518 5,518 6,185 5,643

Heating 3,631 3,544 3,695 3,869

Hot Water 2,860 2,861 3,402 2,862

Total 12,009 11,922 13,282 12,374

All homes visited during the field auditing portion of the study were two-bedroom homes.

Comparative energy models and associated upgrades were performed on a two-bedroom model 
16

as a result. The occupancy assumptions based on the Building America House Simulation 

Protocols Equations 28 and 29 are listed in Table 10 for the Salishan BEopt models (Hendron & 

Engebrecht, 2010). Based on the findings of the field audits and homeowner surveys, the average 

actual occupancy is two to three full-time occupants. As such, occupant dependent usage 

assumptions in BEopt seem appropriate. A three-bedroom unit comparative model was also run 

to test the impact of increased occupancy, as seen in Table 11. 

Table 10. Calculated Occupancy for Two- and Three-Bedroom Units

Equation

Two-Bedroom 

Number of 

Occupants

Three-Bedroom 

Number of 

Occupants

0.59 × Nbr + 0.87 2.05 2.64

0.92 × Nbr + 0.63 2.47 3.39

where Nbr = number of bedrooms

Table 11. BEopt Estimated Consumption Comparison, Two- and Three-Bedroom Units

2006 Code 975-

ft2 Two-Bedroom

2006 Code 975-

ft2Three-Bedroom

MELs 5518 6079

Heating 3544 3353

Hot Water 2861 3401

Total 11922 12834

During the field audits of Salishan phases 1–6, researchers determined that there were few costeffective improvements that could be made to the building shell. The state of Washington has 

had fairly stringent energy codes in place since 1991. Based on the energy code versions that 

phases 1–6 were built under, the slab floor is insulated to R-10 at 2 ft horizontal (interior 

perimeter) and cannot be cost-effectively fully insulated, the walls are fully insulated 2 × 6 

framing cavities and the attics are insulated to R-38. Building air leakage was found to be 

average for the Northwest region—not classified as “tight” construction, but tight enough that 

additional air sealing would not be cost effective.

Having identified the lack of retrofit opportunities for the existing homes, there are several lost 

opportunities for maximizing building envelope efficiency at time of construction. For 

subsequent phases of construction, careful attention to air sealing details at time of new 

construction can yield a reduction 2.4–3.2 ACH50, as seen in Salishan 7 for little to no increase 

in cost (Gordon, Lubliner, Howard, & Kunkle, 2013). 

Given the fairly efficient building envelope required under the 2003 and 2006 WSEC, the 

measures evaluated for retrofit in Salishan 1–6 are focused on mechanical upgrades, including 

the installation of DHPs and heat pump water heaters (HPWHs). 

The incremental cost for DHPs used in the study was $3000 (Lindsay, 2013); this is slightly less 

than the $3,315 observed in the first year report for new construction at Salishan 7 (Gordon, 
17

Lubliner, Howard, & Kunkle, 2013). The cost-benefit analysis used an incremental cost of 

$1,800 for the HPWHs (based on BEopt cost data).

Cost effectiveness is difficult to evaluate for Salishan given that the investment in improvements 

would be at THA’s cost and the benefit of reduced monthly and annual utility costs would be 

experienced by the occupant. The monthly and annual cost savings of improvement measures 

were calculated using $0.7.4/kWh, based on current costs from the electric utility provider, TPU

(Tacoma Public Utilities). There is a fixed service charge of $4.50 for all separately metered 

apartments. Additionally, TPU offers a 30% low income discount to qualifying households. This 

discount brings the cost per kWh to $0.0518. For purposes of this project, the market rate cost 

per kWh of $0.074 is used.

Table 12 provides the energy usage and cost benefit analysis of retrofit measures in Salishan 1–6.

The scenarios are modeled with and without ventilation systems. The initial runs were performed 

with exhaust only systems operating constantly at ASHRAE 62.2-2010 levels. The actual homes 

observed in the field had operational times far shorter than this. Some whole-house ventilation 

systems were not run at all on a consistent or regular basis. That being the case, a second set of 

runs was performed with no ventilation system running to show the impact on savings. 
18

Table 12. Energy Usage and Cost Benefit of Retrofit Measures in Salishan 1–6 

2006 925-ft2 Base

(Electric Resistance Heat) HPWH DHP

Assumes ASHRAE 62.2-2010 Ventilation System

MELs 5518 5518 5518

Cooling 0 0 63

Heating 3544 4177 874

Hot Water 2861 1449 2865

Total 11922 11144 9320

Reduction in kWh 778 2602

Reduction in % 7% 22%

Incremental Cost $1,800 $3,000

Annual Cost Savings $57.61 $192.58

Monthly Cost Savings $4.80 $16.05

Simple Payback, Years 31.25 15.58

Assumes No Ventilation System Operating

MELs 5437 5413 5437

Cooling 0 0 69

Heating 2933 3489 718

Hot Water 2859 1574 2864

Total 11229 10476 9087

Reduction in kWh 753 2142

Reduction in % 7% 19%

Given that the units in Salishan are fairly low load units to begin with, savings as a result of 

potential upgrades are not dramatic. The reduction in space heating load by installing a DHP is 

the most substantial of the mechanical measures evaluated for retrofit. This brought the heating 

load from 29% of the total energy use annually to 9% (see Figure 7 and Figure 8).
19

Figure 7. Breakdown by load type; 100% electric

Figure 8. Breakdown by load type; 100% DHP
20

If DHPs were to be installed as a retrofit measure at Salishan, the electric resistance heaters in 

the upstairs bedrooms and bathroom would need to remain in place and operating, per 

requirements of the International Residential Code (International Code Council, 2012). Under 

this hybrid scenario, field research conducted in the Pacific Northwest suggests a reduction in 

energy use of approximately 48%, considerably less than suggested by the 100% DHP scenario 

within the BEopt analysis (Ecotope, Inc., 2013).

Ongoing research may explore whether the use of whole house mechanical ventilation fans or 

other strategies can improve the distribution of heat from the DHP to the upstairs bedrooms.

7.5 Utility Billing Analysis

Figure 9 and Figure 10 show the monthly electricity use profiles for two- and three-bedroom 

end units. 

Figure 9. Monthly aggregate electricity use for two-bedroom end units
21

Figure 10. Monthly aggregate electricity use for three-bedroom end units
22

Several observations from the figures can be made:

• Electricity use for Salishan 7 is lower in the winter months, indicating electricity savings 

is due to lower energy use for heating.

• Electricity use in the summer is similar, suggesting that we are not seeing an increase in 

electricity use from the cooling capability of the DHPs. Some of the variation in the 

electricity use of individual units may be due to cooling, but this is not significant enough 

to show up in the aggregate data. 

• Electricity use in the winter of 2012 is higher than 2011 for Salishan 7, but is similar for 

Salishan 1–6 (Gordon, Lubliner, Howard, & Kunkle, 2013). Degree day data indicate 

2012 was slightly warmer than 2011. So the increase in heating electricity use for 

Salishan 7 is counter to what would be expected. This might be an anomaly due to homes 

just being occupied at the end of 2010. It also could indicate that as residents get used to 

operating the DHPs in the main living space and baseboard heaters in the bedrooms, they 

increase heating system use (thermostat settings). This observation needs to be tested 

with additional research. 

These observations also apply to the monthly electricity use for the other comparison groups

(stacked and interior units).

To identify the space heat and base load for each comparison group, regression models of 

electricity use and degree days were developed for each of the comparison groups. The aggregate 

monthly electricity use was normalized to Typical Meteorological Year 3 temperature data. The 

degree day temperature base was varied for each case to obtain the best model.2 The results of 

the weather normalization are shown in Table 13.

 2 Researchers used a spreadsheet regression analysis tool developed by Michael Blasnik. It uses a Bayesian approach 

to select the best balance point based on R-squared and a prior estimate of balance point. The tool uses daily average 

temperature data (in this case from Sea-Tac Airport) to estimate degree days at different base temperatures. 
23

Table 13. Regression Model Results for Each Comparison Group

Regression Model # of Data 

Points

Base Load 

(kWh)

Heating

(kWh)

Total 

(kWh)

Balance 

Point 

Temp. (F)

RSquaredNumber 

of Units3

End Two-Bedroom Salishan 1–6 12 6,998 5,091 12,088 61 0.980 144–152

End Two-Bedroom Salishan 7 12 6,892 2,594 9,486 60 0.983 24–27

Savings (kWh) 106 2,497 2,603

Savings (%) 2% 49% 22%

End Three-Bedroom Salishan 1–6 12 9,048 5,638 14,686 60 0.975 200–213

End Three-Bedroom Salishan 7 12 9,454 2,594 12,048 60 0.955 27–28

Savings (kWh) (406) 3,044 2,638

Savings (%) –4% 54% 18%

Interior Three-Bedroom Salishan 1–6 12 9,271 4,558 13,829 59 0.968 25–27

Interior Three-Bedroom Salishan 7 12 9,312 2,192 11,504 59 0.932 9–10

Savings (kWh) (41) 2,366 2,325

Savings (%) 0% 52% 17%

Stacked Two-Bedroom Salishan 1–6 12 7,372 3,951 11,323 60 0.978 48

Stacked Two-Bedroom Salishan 7 12 7,410 2,531 9,942 61 0.976 11–12

Savings (kWh) (38) 1,420 1,382

Savings (%) –1% 36% 12%

 3 The number of units included in the calculation of the monthly average electricity use varies from month to month.
24

The results for the regression analysis are consistent with the observations for Figure 9 and 

Figure 10. All the electricity savings is for space heating. The estimated space heat savings is 

around 50% for the end and interior units and ranges from 2,366 kWh/year for the interior threebedroom units to 3,044 kWh/year for the end three-bedroom units. The stacked two-bedroom 

units have the lowest space heat savings (1,420 kWh/year, 36%). We might expect this because 

these are smaller units with fewer exterior surfaces. 

There is little difference in the base loads of comparable units in Salishan 1–6 and Salishan 7. 

There does not appear to be an increase in electricity use in Salishan 7 from cooling by the 

DHPs. The three-bedroom units have higher base loads (~9,000+ kWh/year) than the twobedroom units (~7,000+ kWh/year) as we would expect. The base loads are greater than the 

space heat loads in all cases, and are significantly greater for the Salishan 7 units. 

While the space heat electricity savings is large, is the difference in annual electricity use 

between Salishan 7 and Salishan 1–6 significant? There is a fair amount of variation in the 

annual electricity use of the housing units in Salishan 1–7 (Figure 11). Most units use between 

10,000 and 17,000 kWh/year. The highest users consume more than 20,000 kWh/year while the 

lowest use around 5,000/6,000 kWh/year. The average use is 13,976 kWh/year. There are some 

units that did not have enough data to calculate annual use that appear as white spots in the data. 

Figure 11. Annual electricity use of each Salishan 1–7 housing units

The Salishan 7 units (on the far right of Figure 11) appear to have lower electricity use than the 

other housing units. To test whether this difference is significant, we conducted a statistical 

analysis of the annual electricity use for each housing unit for the comparison groups. The results 

of this t-test analysis are shown for each comparison group in Table 14.
25

Table 14. T-Test Results for Each Comparison Group

Comparison Group Data Points 

(Salishan 1–6/7)

Savings 

Mean 

(kWh)

Savings 

(%)

Savings 95% 

Confidence Interval

(kWh)

End Three-Bedroom 132/22 2,869 22.5 1,428–4,309

End Three-Bedroom 192/27 2,818 18.5 1,398–4,238

Interior Three-Bedroom 24/8 2,400 17.0 391–4,408

Stacked Two-Bedroom 46/10 1,622 13.6 –343–3,586

The t-test analysis indicates annual electricity use for the two- and three-bedroom end units in 

Salishan 7 is clearly lower than Salishan 1–6 and there are energy savings. The savings are 

estimated to be 1,400 to 4,300 kWh/year at 95% confidence. These results are a strong indicator 

of the benefits from the Salishan 7 energy efficiency improvements. 

The electricity use for the interior three-bedroom units for Salishan 7 is also statistically less than 

Salishan 1–6 at 95% confidence, although the confidence interval is wider and nears zero at the 

lower end. For the stacked two-bedroom units, the 95% confidence interval is slightly negative. 

For this particular comparison group, statistical significance is a little less than 95% confidence. 

Because the samples for these last two comparison groups are small, the results are more prone 

to be skewed by other factors besides the Salishan 7 energy efficiency improvements. 

The annual savings results in Table 14 are very similar to the results from the regression analysis 

shown in Table 13. The regression analysis results for the two- and three-bedroom end units are 

22% and 18% savings, the interior three-bedroom 17%, and the stacked two-bedroom 12%. The 

magnitude of the electricity use and savings is a little less for the regression analysis, which uses 

Typical Meteorological Year 3 weather data (typical year). This is the expected result since the 

actual 2012 weather was a little cooler than a typical year. 

The fact that the different utility bill analyses produce comparable results adds confidence to the 

conclusion from the Year one report that the LEED Platinum Salishan 7 units use significantly 

less electricity than the units built to the WSEC in Salishan phases 1–6 (Gordon, Lubliner, 

Howard, & Kunkle, 2013). This savings is from a reduction in space heating electricity use on 

the order of 50%. There is no evidence that the cooling capability of the DHPs is adding to the 

average summer electricity use of the Salishan 7 units. The base load (non-space heating) 

electricity use is generally greater than the space heating use in all cases. This is particularly true 

for Salishan 7, where space heat loads are around 20%–25% of total electricity use. 

7.6 Utility Model and Energy Simulation Model Comparison

Comparison of utility regression models to the energy simulation models yielded fairly good 

alignment for estimated whole-house electricity use. The difference between the regression 

model and simulation model for Salishan 1–6 was 166kWh, or 1.37%. As shown in Table 15, the 

difference between the regression model and simulation for Salishan 7 was 460 kWh, or 4.48% 

indicating that the energy simulation modeling is representative of whole-house electricity usage 

at the Salishan development.
26

Table 15. BEopt Model Compared to Utility Regression Model

Utility 

Regression 

Model

Energy 

Simulation 

Model

Difference 

(kWh)

Difference of Model 

From Utility 

(%)

Salishan 1–6 12,088 11,922 166 1.37%

Salishan 7 9,486 9,026 460 4.84%

However, comparing the breakdown of base load and heating load estimates between the BEopt 

energy simulation model and the regression model, alignment by category is not as favorable. 

These results, shown in Table 16, indicate that for Salishan phases 1–7, the BEopt model is 

overpredicting the base load and underpredicting heating load.

Table 16. BEopt Model Compared to Utility Regression Model, Base Load, and Heating Load

Base Load Heating Total

Salishan 1–6 BEopt 8,467 3,455 11,922

Salishan 1–6 Regression 6,998 5,091 12,088

Difference of BEopt From Regression –1,469 1,636 166

Salishan 7 BEopt 8,531 495 9,026

Salishan 7 Regression 6,892 2,594 9,486

Difference of BEopt From Regression –1,639 2,099 460
27

8 Conclusions

1. How does the modeled energy use (using BEopt) for Salishan phases 1–6 compare to the 

actual use derived from billing data?

Total modeled energy usage for Salishan phases 1–6 was 11,922 kWh/year, with 3,544 

kWh/year for heating, or 29% of total energy usage.

The billing analysis suggests annual energy use of the two-bedroom duplex (comparable to 

the unit modeled with BEopt) to be 12,088 kWh, with 5,091 kWh from heating. While the 

BEopt model and utility billing analysis yielded good alignment overall (a difference of 166 

kWh or 1.37% for total energy use), the heating load estimates were not well aligned, with a 

difference of 1,469 kWh or 21%, suggesting that the BEopt analysis may be overpredicting 

base load and underpredicting heating load.

2. How do phases 1–6 compare to phase 7?

A comparison of annual energy usage (from billing analysis) between Salishan phases 1–6

and Salishan 7 indicates savings of 1,400 to 4,300 kWh/year, a strong indicator of the 

benefits from the Salishan 7 energy efficiency improvements. 

3. What are the opportunities for energy efficiency retrofit improvements in Salishan phases 1–

6?

If 100% of the existing electric resistance heating is assumed by the DHP, energy savings is 

predicted to be 2,602 kWh annually; this amounts to $193 in cost savings, and a 15-year 

payback (well within the expected life of the equipment). If the displacement level of the 

electric resistance heating is less than 100%, the savings and payback are reduced. Based on 

DHP retrofit research conducted in the Pacific Northwest (used in previous Building America 

projects), these savings may be reduced by as much as 60%. 

The analysis of HPWHs suggests annual savings of 778 kWh, or $58. Using current 

incremental cost assumptions, payback for the HPWH does not fall within the useful life of 

the system. However, the installation of HPWHs may be justified for homes with high base

load use and high occupancy (a surrogate for high domestic water heating usage). Combining 

the installation of HPWHs and DHP retrofits may improve cost effectiveness and installation 

logistics in occupied dwellings.

4. How do the mechanical ventilation systems perform compared with Washington Statemandated requirements and ASHRAE 62.2-2010, and how did field assessments and 

occupant surveys reflect the operation of the systems?

All audited units have ventilation systems capable of meeting VIAQ or ASHRAE 62.2-2010 

requirements (in terms of fan flow), though runtimes varied. None of the tenants seemed to 

have a working knowledge of their ventilation systems.
28

5. What are the measured temperature and RH levels in the homes during the heating season, 

and what impact did they have on occupant comfort?

Average hourly indoor temperatures were 73°F for the monitoring period November 2012 to 

March 2013. The monitoring data do suggest high temperature swings in each home (as 

much as 31°F difference between minimum and maximum monitored temperatures).

Occupant surveys indicated a high degree of variability of satisfaction with the comfort level 

in their homes; the high degree of variability in the monitored temperatures further reflects 

this.

Average hourly RH levels were 40% for the monitoring period, suggesting good humidity 

control with well operating whole-house fans and with air change rates typical for new 

construction (5–7 ACH50).
29

9 Recommendations

• If the DHPs can be acquired by King County Housing Authority (KCHA) at the price 

assumed in the analysis, they should be considered for future retrofit efforts, particularly 

for homeowners with high space heat use, or who express concerns about comfort with 

the use of the resistance heat. Additional benefit may be seen by tenants with a need for 

air conditioning (for example, seniors, or tenants with special health needs). At the 

assumed cost, the DHP could pay back within its expected life (15–20 years).

• The use of the HPWH in retrofit efforts is more questionable. At the assumed cost, the 

HPWH does not pay back within its expected life. TPU billing data can identify units 

with high base load use as candidates for HPWH retrofits.

• In the course of routine maintenance, KCHA staff can verify that the whole-house 

ventilation systems are set up correctly, to either VIAQ or ASHRAE specifications, and 

neither under- nor overventilating. KCHA staff can also use the opportunity to educate 

tenants on the purpose and correct operation of their ventilation systems.
30

10 Potential Research Opportunities

• Additional research is needed to confirm whether the electric resistance displacement 

assumptions used in Pacific Northwest DHP studies is consistent with low-load, high 

efficiency housing such as Salishan phases 1–6. A pilot project by THA and TPU could 

identify dwellings that would be good candidates for retrofits (homes with high space 

heating use, determined through billing analysis).The pilot project can also investigate 

changes in RH and temperature pre- and post- DHP retrofit.

• Further research is warranted into the proper modeling in BEopt and other single-zone 

hourly simulation models of multizone hybrid space heating systems, utilizing DHPs and 

electric resistance heat. 
31 

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Ecotope, Inc. (2013). Ductless Heat Pump Impact and Process Evaluation: Billing Analysis 

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Johnson, D. (2012, June 20). Salishan superintendent, Walsh Construction. (A. Gordon, 

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Retrieved December 12, 2013, from RESNET: 

www.resnet.us/standards/RESNET_Mortgage_Industry_National_HERS_Standards.pdf 

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2012, from Tacoma Housing Authority: www.tacomahousing.org/Salishan/history.html 

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32 

Appendix A: Audit Forms
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34 

Appendix B: Occupant Survey
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36
DOE/GO-102014-4348 ▪ April 2014

Printed with a renewable-source ink on paper containing at 

least 50% wastepaper, including 10% post-consumer waste.

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